(1) Field of the Invention
The present invention relates to a technology for defining the space between a TFT substrate and a facing substrate in a liquid crystal display using a support pillar system.
(2) Related Art Statement
In liquid crystal display devices, the space between the TFT substrate on which pixel electrodes and thin film transistors (TFT's) are formed and the facing substrate on which color filters and the like are formed is filled in with liquid crystal so that an image is formed by controlling the molecules of this liquid crystal by means of an electrical field. The space between the TFT substrate and the facing substrate is as small as several microns. It is extremely important to set an appropriate space between the TFT substrate and the facing substrate in order to control the transmission of light through the liquid crystal.
The space between the TFT substrate and the facing substrate in conventional liquid crystal display devices is created by dispersing beads or the like. When beads are dispersed, however, beads are also provided in regions where pixel electrodes are formed, and such a problem arises that light is scattered in these portions and the contrast lowers.
Meanwhile, conventional methods that have been developed for filling the space between the substrates with liquid crystal include: a method for sealing the space between the TFT substrate and the facing substrate, providing an opening in a portion of the sealing material, and injecting liquid crystal through the opening; and a method for dropping a necessary amount of liquid crystal onto the TFT substrate, and after that pasting the facing substrate so as to seal the liquid crystal. In any cases where beads are dispersed, the beads move, creating locations where there are many beads and locations where there are few beads when the liquid crystal is dropped. In addition, beads are dispersed into regions with pixels through which light from the backlight transmits, and this may cause a lowering of the open area ratio.
In order to solve the above described problem, a method for forming support pillars of an organic film on the facing substrate (support pillar system) has been developed as a method for defining the space between the TFT substrate and the facing substrate. Support pillars can be provided in portions where there are no pixel electrodes, that is to say, portions through which light from the backlight transmits. Accordingly, the brightness (the open area ratio) is not lowered. In addition, the support pillars are fixed to the facing substrate, and thus do not move when liquid crystal is dropped. Accordingly, the method for maintaining the space with support pillars is preferable for a system where liquid crystal is dropped (liquid crystal dropping and sealing system).
In general, these support pillars are formed on a black matrix on the facing substrate. The support pillars are formed of a resin, such as acryl, and one photolithographic step is required in order to form these support pillars according to the prior art. “Patent Document 1” describes a technology for forming multilayer support pillars of color filters in order to omit the photolithographic step of creating support pillars.
Meanwhile, in the case where multilayer support pillars are formed of color filters, color filters for each color must be precisely positioned in the support pillar portions; otherwise, the height of the support pillars becomes inconsistent. As a measure against this problem, “Patent Document 2” describes a technology for keeping the height of the support pillars constant by using color filters of which the form in plane is rectangular as the support pillars, and changing the orientation of the longitudinal axis of the rectangles by 90 degrees every time color filters are layered.
[Patent Document 1] Japanese Unexamined Patent Publication H9 (1997)-499914
[Patent Document 2] Japanese Unexamined Patent Publication 2003-233064